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Forensic Podiatry (Part Two of Two)

Written by John A. DiMaggio, DPM

THE DISCIPLINE of forensic podiatry—or, in other words, the examination of pedal evidence—has progressed significantly over the past ten years. It is no longer a question of “What can you do with a footprint?” but rather, “Who can we use to evaluate the footprint?” Cases involving pedal evidence, especially bloody footprints and issues of determining shoe sizing or fit issues compared to questioned footwear, have become more common over the past two or three years.

This is a diagram of a bare footprint and its outline. On the left are shown identification lines that are used by forensic podiatrists: (1) web space outline; (2) web ridge lines; (3) arch line; (4) lateral foot line; and (5) heel line. On the right are the foot zones and their relative sizes: (6) forefoot—40%; (7) mid-foot—30%; and (8) rearfoot—30%.

It must be understood that I do not claim to be an expert in the techniques or use of the devices described here, and can only speak about these techniques to the extent of my own training and personal knowledge. You will find this to be true with any professional you work with in the field, and this is where the team approach is so important: It allows you to combine the knowledge and expertise from different individuals to facilitate the best possible outcome. This is also an opportunity for a crime-lab technician or criminalist to be innovative through experimentation and to discover new techniques that increase the potential for utilizing evidence which, until recently, was not deemed of value.

Footprints at the crime scene

Evidence collection is one of the most important components of a criminal investigation and subsequent prosecution. Physical evidence can positively link a suspect to a crime, or it can prove one’s innocence.

Advancements in technology and instrumentation have assisted law enforcement with its ability to collect forensic evidence.
Crime-scene processing and evidence collection has become even more important recently, possibly due to the increased awareness by the general public of techniques that are often shown on television programs, creating the additional burden for real-life professionals in the field to solve crimes in a similar manner. Items that may or may not have evidentiary value need to be discovered, identified, collected, and analyzed. Luckily, this important task has been assisted by continual technological advances.
The crime laboratory can offer assistance in certain areas when physical evidence is transported to the lab.

General concernsregarding pedal evidence

There is a belief regarding pedal evidence that if there is one footprint then there should be more. Why is it that only one is found—or, in some cases, none at all? In the not-too-distant past, this kind of evidence was not considered of much value, especially if there were no suspects. In addition, it was widely believed that pedal evidence either lacked any significant importance or was completely unusable.

With the introduction of certified footwear examiners and forensic pod-iatrists, that mindset should be revised. The investigator needs be looking for pedal evidence immediately upon entering the crime scene and take appropriate action to locate and preserve that evidence.

In many cases, the crime scene is chaotic. There may be multiple crime-scene footprints that in part were left by first responders such as EMTs or police officers—but it is better for you to collect and exclude later than not to collect at all. There is always the chance that one of those prints belongs to the suspect. It must be remembered that every footprint has the potential for providing information about the individual who made it because of the uniqueness of every footprint, including differences between the right and left foot of the same person.

In addition to the obvious areas—such as walkways and building entryways—a systematic search needs to be performed, especially in exterior areas.

Collection of pedal evidence at the crime scene

Once the pedal evidence has been discovered and documented, one must consider the best methods of collecting that evidence. It is always advantageous to collect the original on-site footprints and transport them to the laboratory for further evaluation.

The tools that are used for footwear-impression and pedal evidence are very similar (Table 1 on Page 38). For a more complete listing and a complete discussion of specific techniques, the reader is referred to other sources, such as the book by Dwane S. Hilderbrand, Footwear: The Missed Evidence (2007).

When photographing pedal evidence, the challenge is using techniques that make the prints or impressions more visible to the camera. Because of trace residue that is often present, standard lighting techniques for photographing pedal evidence are usually not satisfactory. Instead, the most successful method of obtaining the best representation of the pedal evidence is to hold a bright light at an oblique angle.

Additional enhancement at the scene may be necessary, especially with blood-origin impressions—and sometimes transporting the on-site evidence to the laboratory for further evaluation is also advantageous.

Different chemical agents can be used for enhancing bloody footprints that are visible or nearly latent. Leuco- crystal violet (LCV) and amido black are commonly used for this purpose. Luminol is one chemical that can be utilized for bloody latent footprints and can even help identify footprints at a scene that have been washed clean by a perpetrator in an attempt to remove the evidence. A forensic light source with fluorescent powder or a RUVIS (Reflected Ultraviolet Imaging System) may be helpful to uncover footprints utilizing similar techniques that are used for fingerprint evidence.

Lifting two-dimensional impressions

The conditions and situations will vary from crime scene to crime scene. This is where the criminalist’s training and experience comes into play, requiring careful consideration of what techniques are available and which ones work best in any given situation.
A surface may be hard, dry, damp, wet, muddy, porous, or non-porous, and the origin of the residue may be dry or moist. The conditions may not always be optimal for successfully lifting usable prints. Because of the difficulty in utilizing lifting techniques for footprint impressions in blood, these kinds of prints are best photo-graphed and enhanced as needed for better photographic representation.

The most commonly used supplies for lifting include white adhesive-lifters and black or white gelatin lifters. Powdering techniques can also be used with appropriate lifting materials.

The electrostatic dust lifter is also an important tool in the criminalist’s arsenal. This device was originally utilized for examining questioned documents for indented writing. The device was also found to be successful for lifting dry-residue footwear impressions at the crime scene. The dust print is transferred to the dark-colored lifting film, allowing it to be photographed. The surface must be relatively clean and the impression must be composed of a dry material (such as gravel dust). One advantage is that it can be used on any surface, whether porous or nonporous. An electrostatic dust lifter even enables the criminalist to obtain a lift from carpet.
The dust lifter has mostly been used for footwear impressions, but there is no reason why it cannot be used for barefoot or sock-clad foot impressions that are composed of a residue transferred in a similar manner as that from footwear.

Recovering three-dimensional pedal impressions

This is an important technique to use at crime scenes when impression evidence is found. All three-dimensional footprint impressions should be cast. The current material utilized is easily prepared at the crime scene and available in prepackaged quantities to which water is added and mixed in the plastic bag. It creates a very hard cast that can be easily transported and used for court exhibit, if needed, without the fear of it breaking (a problem that was very common with plaster of Paris casts). Having a cast of a footprint or shoeprint—as opposed to only having photos available for examination—can be extremely important when sizing issues are of concern.

Snow-print wax can be utilized for impressions in snow. The aerosol is sprayed into the impression before it is filled with dental stone. This significantly aids in getting a better representation of the impression.

Analysis techniques in the crime laboratory

A forensic light source is a light that combines powerful illumination with optimum wavelengths. It utilizes either a 300- or 500-watt xenon arc lamp or halogen lamp. It can be tuned to output ultraviolet (UV), visible light, or infrared, depending on the device. Ultraviolet wavelengths of 365 nm are often used with certain fingerprint-enhancement processes, including visualizing and photographing fluorescent fingerprint powder. (For more on the use of light sources, see “The basic theory behind alternate light sources,” Evidence Technology Magazine, January-February 2008, Vol. 6 No. 1, Pages 30-33.)

One area of importance for pedal evidence is the evaluation of the sock liner (commonly called insole) that is often needed to help determine foot-wear ownership, or to address questions regarding the predominant wearer of the shoe. The image of the foot reproduced on the sock liner image can be better visualized through enhancement techniques carried out in the crime laboratory where the time can be taken, for example, to systematically go through the different wavelengths.

Because of the variability of top-cover colors, the contrast can be poor, especially with darker colors. An image of a foot in the sock liner (Figure 1), in addition to being caused by the weight-bearing stresses, is influenced by ambient conditions and the amount of foot perspiration, something that varies between individuals.

Figure 1

A number of years ago, I became interested in techniques to enhance the image on the sock liner. At that time, I worked with SPEX Forensics utilizing a CrimeScope CS-16 forensic light source. I experimented with various techniques, including dyes and stains consisting in part of Basic Yellow 40, Small Particle Reagent, and Nile Red. Cyanoacrylate (CA) fuming was also performed on the sock liners prior to the chemical treatments.

In one of the experiments, the sock liner’s top cover was very dark in color—a shade that often does not lend itself to a usable footprint image. The sock liner was CA-fumed for 30 minutes at 80% relative humidity. Basic Yellow 40 was applied and rinsed with methanol. Excitation was found at 455 nm using the CS-16 forensic light source. It was photographed using the SPEX CrimeScope VRM with an orange long-pass filter or 550 nm band-pass filter.

There is a lot of potential in this area for increasing the quality of the footprint image for the best possible examination purposes. This importance is evident when identification lines are used for comparison purposes, as discussed later.
On some sock liners, the examiner actually has a three-dimensional impression to work with. If needed, it is possible to utilize a thin layer of dental stone to make a thin cast showing the digital positioning.

There has been some success looking at bruising on the human body, usually at shorter wavelengths in the UV range. This could be helpful in identifying a footprint on a body.

Equipment and chemicals used by the forensic podiatrist

The tools that are used by a forensic podiatrist are, in many cases, used for the construction of the known exemplars. If one has the interest or ability, the forensic podiatrist can also assist in using an electrostatic dust lifter or a forensic light source for enhancing the sock-liner image. It would also be appropriate at times for the forensic podiatrist to be called to the crime scene to assist in identifying and collecting pedal evidence.

Table 2 on Page 39 lists some equip-ment and chemicals that may be used by the podiatrist. The most commonly utilized will be briefly discussed here.

The inkless shoe-print kits available through Forensics Source and other vendors is easy to use, does not make a mess, and is more easily utilized in a wide variety of situations. A two-step method according to protocol is utilized to give a dynamic footprint with an outline of the foot, showing the foot morphology.

The PedoGRID System is a device that was developed strictly for pedal applications, but can be used for other applications where measurements are necessary. It is constructed on an 11 x 17-in. sheet of clear vinyl plastic—.010-in. thick—that is durable and easily transportable. It is composed of a millimeter grid system that sits side-by-side with a shoe-measuring system. A foot can be measured directly (Figure 2), but it can easily be used to overlay a foot mold or a bare footprint at the crime scene, for example. Obviously, any reading is an approximation of shoe size only. Variables encountered are within the purview of the expert’s opinions.

Figure 2

The podiatrist often utilizes foam impression material when taking weight-bearing exemplars from the suspect. This material is available from different sources and gives an excellent representation of the weight-bearing foot. Usually, no friction-ridge skin will be visible in the impression. There are some plastic impression materials that can be molded to the bottom of the foot that give excellent ridge patterns if that level of detail is a concern.

Force-plate devicesfor imaging foot pressure

A technological device that has been utilized in podiatric medical practice for a number of years is called a force- plate system that can be used as a static system with dynamic capabilities, or as a mobile system. The system the author is most familiar with is the mini-EMED system, manufactured by Novel GmbH in Munich, Germany (Figure 3). It is an electronic measurement system for recording and evaluating pressure distribution of flat and curved surfaces. It is used to gather information on ground-reactive force and gait. It records and displays graphically the dynamic pressure distribution of the stationary foot but, more importantly, it can also take measurements of a foot in motion.

Figure 3

During static operation, the footprint is examined and the maximum pressure (n/cm2) is calculated as well as the total force (n) and footprint area (cm2). In the dynamic mode, roll-off motion is automatically reanimated in a color monitor. The unit indicates the progress of total force, the maximum pressure, and the footprint area over time (Figure 4). Both results can then be reproduced in actual size, or a 1:1 ratio (Figure 5).

Figures 4 and 5

A dynamic system—the Pedar, also manufactured by Novel GmbH—uses a foot sensor that is placed in a shoe and records data while the subject is walking. Some of the medical indications include determining weight-bearing areas of the bottom of the foot that are more prone to excess forces creating ulcers (sores) or other lesions prone to cause foot pathology.

Forensic implications include a case where pressure distribution on a sock liner or in a bloody footprint is called in question. Taking measurements on a suspect would provide data about the pressure on the bottom of the foot in specific areas—data that could also be correlated to the other findings. This may in fact be another method to substantiate other findings, but in some cases in particular it could be used where a specific lesion is noted on the bottom of the foot since this device provides the ability to quantify the findings graphically. As more pedal cases are evaluated, the greater potential for its use exists.

Examination of physical evidence

A forensic podiatrist utilizes various methodologies in order to analyze questioned physical evidence. This involves breaking it down and dissecting it into its component parts that can be best used for comparison purposes.

Some of the things a forensic podiatrist looks for are class, intermediate, and unique characteristics. The foot offers different and more complex characteristics compared to other objects. Class characteristics for the foot include the toes and arch or the ball and heel areas.

Unique characteristics are certainly more rare on the bottom of the bare foot in comparison to the possibilities for the shoe outsole. One example of a unique characteristic on the bare foot would be the presence of a hard skin area on the bottom surface of the foot resulting from a nail puncture. A unique area of this sort could be visible on the sock liner of the shoe or in a bloody footprint.

Intermediate characteristics are not unique but, in the aggregate, they can lead the examiner to a higher level of certainty. Examples include a bunion (bump on outside of big toe joint with malposition of the toe) and hammer-toe deformity (contracture of the toe with malposition). The identification lines or foot zones can also be used, if applicable. The identification lines include the arch line, heel line, and web-ridge line. The foot zones—which consist of the rear-foot (the rear 30%), mid-foot (the middle 30%), and forefoot (the front 40%)—can be very helpful in determining proportion-ality of the foot image, especially if the foot-print is dynamic in origin.

Comparison techniques involve taking measurements of the known impression—for example, the length from the heel to the farthest extension of each toe and a multitude of other points of reference—and comparing them to measurements of the unknown impression in order to note similarities or dissimilarities.

Most commonly, however, forensic podiatrists utilize overlay techniques. Depending on the quality and quantity available from a photograph of a questioned footprint at the crime scene, for example, the aggregate of findings can be applied to the levels of certainty.

There are many other possibilities when it comes to different scenarios. For example, when making comparisons involving the sock liner of the shoe, further examination of the shoe, relative to the upper, may present the examiner with wear marks secondary to a hammertoe deformity that creates an outward bulge in the shoe and a corresponding wear area on the inside upper at that location. The shoe can be cut and the upper flipped open to show the relationship between a questioned shoe and a suspect’s foot.
Ultimately, a conclusion must be drawn. Both negative and positive evaluation findings are then related to the levels of certainty (Table 3 on Page 39). If the findings are on the negative side, a determination of exclusion is drawn. On the affirmative side, it could be determined an inconclusive, or it could be elevated to the higher levels of certainty. In most cases, this author seeks verification by another examiner.

As with any conclusion, of course, the weight of the findings will then be determined by the jury.

Some final thoughts about how you might approach forensic podiatry

It has been the intent of this article to introduce the relatively new discipline of forensic podiatry and the tasks that the podiatrist performs in the most basic form. As with any discipline, the findings of a forensic podiatrist do not stand alone. Other specialists that could be involved in pedal cases include the forensic anthropologist, professional tracker (specializing in tracking humans), and the footwear examiner.

The forensic podiatrist must be well trained in scientific methodology, have a broad knowledge of the field, demonstrate the ability to work with others in associated fields, and be able to testify and formulate conclusions in an objective manner.
If you have any questions about anything that was touched upon in this article, please contact me. mmm
About the Author

John A. DiMaggio, DPM, is a forensic podiatrist with Forensic Podiatry Con-sulting Services, PLLC, in Bandon, Oregon. Before working with his podiatry practice, he was a certified reserve police officer for 15 years in Mesa, Arizona. During that time, he worked with crime-scene officers where he participated in training and gained field experience with crime-scene processing.

He can be reached by e-mail:
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Or by telephone at this number: 541-347-3632

ORIGINALLY PUBLISHED:
"Forensic Podiatry (Part Two of Two)," written by John A. DiMaggio
May-June 2008 (Volume 6, Number 3)Evidence Technology MagazineBuy Back Issue

Most forensic disciplines attempt to determine the “who” of a crime. But bloodstain pattern analysis focuses on the “what happened” part of a crime. This book is the third edition of Blood-stain Pattern Analysis. The authors explore the topic in depth, explaining what it is, how it is used, and the practical methodologies that are employed to achieve defensible results. It offers practical, common-sense advice and tips for both novices and professionals. www.crcpress.com